servers/mfs/buf.h

   1 /* Buffer (block) cache.  To acquire a block, a routine calls get_block(),
   2  * telling which block it wants.  The block is then regarded as "in use"
   3  * and has its 'b_count' field incremented.  All the blocks that are not
   4  * in use are chained together in an LRU list, with 'front' pointing
   5  * to the least recently used block, and 'rear' to the most recently used
   6  * block.  A reverse chain, using the field b_prev is also maintained.
   7  * Usage for LRU is measured by the time the put_block() is done.  The second
   8  * parameter to put_block() can violate the LRU order and put a block on the
   9  * front of the list, if it will probably not be needed soon.  If a block
  10  * is modified, the modifying routine must set b_dirt to DIRTY, so the block
  11  * will eventually be rewritten to the disk.
  12  */
  13
  14 #include <sys/dir.h>                    /* need struct direct */
  15 #include <dirent.h>
  16
  17 EXTERN struct buf {
  18   /* Data portion of the buffer. */
  19   union {
  20     char b__data[_MAX_BLOCK_SIZE];                   /* ordinary user data */
  21 /* directory block */
  22     struct direct b__dir[NR_DIR_ENTRIES(_MAX_BLOCK_SIZE)];
  23 /* V1 indirect block */
  24     zone1_t b__v1_ind[V1_INDIRECTS];
  25 /* V2 indirect block */
  26     zone_t  b__v2_ind[V2_INDIRECTS(_MAX_BLOCK_SIZE)];
  27 /* V1 inode block */
  28     d1_inode b__v1_ino[V1_INODES_PER_BLOCK];
  29 /* V2 inode block */
  30     d2_inode b__v2_ino[V2_INODES_PER_BLOCK(_MAX_BLOCK_SIZE)];
  31 /* bit map block */
  32     bitchunk_t b__bitmap[FS_BITMAP_CHUNKS(_MAX_BLOCK_SIZE)];
  33   } b;
  34
  35   /* Header portion of the buffer. */
  36   struct buf *b_next;           /* used to link all free bufs in a chain */
  37   struct buf *b_prev;           /* used to link all free bufs the other way */
  38   struct buf *b_hash;           /* used to link bufs on hash chains */
  39   block_t b_blocknr;            /* block number of its (minor) device */
  40   dev_t b_dev;                  /* major | minor device where block resides */
  41   char b_dirt;                  /* CLEAN or DIRTY */
  42   char b_count;                 /* number of users of this buffer */
  43 } buf[NR_BUFS];
  44
  45 /* A block is free if b_dev == NO_DEV. */
  46
  47 #define NIL_BUF ((struct buf *) 0)      /* indicates absence of a buffer */
  48
  49 /* These defs make it possible to use to bp->b_data instead of bp->b.b__data */
  50 #define b_data   b.b__data
  51 #define b_dir    b.b__dir
  52 #define b_v1_ind b.b__v1_ind
  53 #define b_v2_ind b.b__v2_ind
  54 #define b_v1_ino b.b__v1_ino
  55 #define b_v2_ino b.b__v2_ino
  56 #define b_bitmap b.b__bitmap
  57
  58 EXTERN struct buf *buf_hash[NR_BUF_HASH];       /* the buffer hash table */
  59
  60 EXTERN struct buf *front;       /* points to least recently used free block */
  61 EXTERN struct buf *rear;        /* points to most recently used free block */
  62 EXTERN int bufs_in_use;         /* # bufs currently in use (not on free list)*/
  63
  64 /* When a block is released, the type of usage is passed to put_block(). */
  65 #define WRITE_IMMED   0100 /* block should be written to disk now */
  66 #define ONE_SHOT      0200 /* set if block not likely to be needed soon */
  67
  68 #define INODE_BLOCK        0                             /* inode block */
  69 #define DIRECTORY_BLOCK    1                             /* directory block */
  70 #define INDIRECT_BLOCK     2                             /* pointer block */
  71 #define MAP_BLOCK          3                             /* bit map */
  72 #define FULL_DATA_BLOCK    5                             /* data, fully used */
  73 #define PARTIAL_DATA_BLOCK 6                             /* data, partly used*/
  74
  75 #define HASH_MASK (NR_BUF_HASH - 1)     /* mask for hashing block numbers */